Maximizing the Accuracy of Double Probe Electric Field Measurements Near Perigee: The Case of the Van Allen Probes Instruments

The Van Allen Probes spacecraft flew through the inner radiation belt and the plasmasphere, probing the extremely dynamic coupling between the thermosphere, the ionosphere and the subauroral magnetosphere. Examining the electrodynamics of this region using Van Allen Probes data required that the ∼1 mV/m electric field (E-field) of interest be measured in a region where the E-field due to spacecraft motion was ∼100 mV/m. This means that the E-field, the magnetic field, and the spacecraft velocity had to be measured to better than 1%. The instruments on board the Van Allen Probes have achieved this accuracy, delivering reliable near equatorial E-field measurements even below three Earth radii. The objective of this commentary is to summarize the methodology developed over the years to maximize the accuracy and scientific return of these double probe E-field measurements below L = 3.